"ecologically" steep and groups of species have fairly similar tolerance 

 that tend to group them on these gradients (Mitsch and Gosselink 1986) . 

 Gleason's individualistic hypothesis can be supported by several 

 studies (Curtis and Mcintosh 1951; Brown and Curtis 1952; Bray 1956; 

 Whittaker 1956; Curtis 1959; Whittaker and Niering 1965; and Mohler 

 1979) . These studies show that although species have different ecologi- 

 cal amplitudes and, in fact, do not occupy the same niche, they organize 

 as units based on similar ecological conditions. Moreover, intergrades 

 caused by interspecific competition occur between defined types of plant 

 associations. These intergrades can be attributed to continuous envi- 

 ronmental variability in time or space or to environmental modification. 



Bottomland Forest Community Organization 



Van Der Valk (1981) developed a qualitative model of succession in 

 freshwater wetlands based on the "individualistic" approach to vegeta- 

 tion proposed by Gleason. He based his approach on three key life his- 

 tory features of plant species: life-span, propagule longevity, and 

 propagule establishment requirements. These features are all directly 

 affected by the flooding on bottomland forests. 



Brinson (1990) , in discussing the "power line" designation for a 

 wetland classification developed by Kangas (1990), considered the power 

 and frequency of inundation as the way in which flood events organize 

 the plant communities in riverine forests. He characterized the flood 

 events as high, medium, and low power events with flood power and fre- 

 quency of inundation being inversely proportional. High power flood 

 events have a low frequency and determine patterns of the large flood- 

 plains features (e.g., oxbow lakes, relict levees, and low ridges and 



